On-wafer electronic devices, such as integrated circuits, or semiconductors, can be operationally tested by connecting a device under test (“DUT”) to a test apparatus using cobra probes. Cobra probes are wires mounted in parallel with two plates which extend transversely to the long axes of the wires, their respective ends are terminated at a probe interface board (i.e., PIB) at top and the on-wafer DUT at bottom. The wires are pre-shaped in a curve so that they flex in a predetermined direction in response to an axial force. Electrical contacts at the ends of the cobra probes align with guide holes formed in the said two plates, an upper plate (i.e., upper die) and a lower plate (i.e., lower die). Upon depression of moving the wafer to the PIB, the electrical contacts are pressed against contact pads of both the PIB and the DUT to produce a temporary electrical connection with the test apparatus.
When connected to a DUT, the cobra probes become part of a circuit in which the cobra probes act as parasitic inductors. The amount of inductance corresponds to the cobra probes' physical dimensions (e.g., wire lengths). The effective inductance of the cobra probes can range from several nanohenries (nH) to tens of nH. In direct current (DC) and low frequency tests, the effects of the probes' inductance can be ignored. However, for DUTs that operate at high-frequencies (e.g., greater than several hundred megahertz), the inductance of the cobra probes may cause grounding and signal integrity issues. As such, the frequency range in which cobra probes can be used is normally limited to circumstances where their inductance is negligible. More specifically, the cobra probes' effective operational bandwidth can be quantified as frequency range in which insertion loss is less than 1 dB and return loss is greater than 10 dB. In other words, the through power loss due to a probe is less than 20% and the reflection power loss is less than 10%.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.